Packaging & Yield

Plastic or ceramic packaging involves mounting the die, connecting the die pads to the pins on the package, and sealing the die. Tiny wires are used to connect pads to the pins. In the old days, wires were attached by hand, but now purpose-built machines perform the task. Traditionally, the wires to the chips were gold, leading to a "lead frame" (pronounced "leed frame") of copper, that had been plated with solder, a mixture of tin and lead. Lead is poisonous, so lead-free "lead frames" are now mandated by ROHS. Chip-scale package (CSP) is another packaging technology. A plastic dual in-line package, like most packages, is many times larger than the actual die hidden inside, whereas CSP chips are nearly the size of the die. CSP can be constructed for each die before the wafer is diced. The packaged chips are retested to ensure that they were not damaged during packaging and that the die-to-pin interconnect operation was performed correctly. A laser etches the chip's name and numbers on the package. 

Integrated Circuits packaging encloses the die in protective package. IC packaging forms the leads on the leadframe to interconnect the chip bonding pads with the second level assembly circuit board. Chip bond pads on a pitch ranging from 60 to 115. The lead frame leads fan out from this bonding pad to the larger pas pitch used on the circuit boards. A relatively large pitch is used on the circuit board ranging from about 12 miles up to 25 to 50 mils for the surface mount compontents.

The packaging of the IC is necessary because it serves four important functions for all types of chips,

• protection from the environment and handling damage.
• Interconnections for the signals into and out of chip.
• Physical support for the chip.
• Heat dissipation. 

The package is selected so that the four functions are optimized to meet certain design constraints: performance, size, weight, weight, reliability, and cost objectives. There are many techniques for packing the integrated circuits. Few of them are discussed in the next subsections.